It was the park's first fatal grizzly mauling since 1986, but the third in the Yellowstone region in just over a year amid ever-growing numbers of grizzlies and tourists roaming the same wild landscape of scalding-hot geysers and sweeping mountain vistas.

Wednesday's attack happened just two days after the peak weekend for tourism in the park all year, on a trail close to Canyon Village, Wyoming, near the middle of Yellowstone.

Park officials said the bear attacked to defend against a perceived threat. They said the wife of the 57-year-old victim called emergency services on her mobile phone and other hikers in the area responded to her cries for help.

Yellowstone spokesman Al Nash said the couple saw the bear twice on their hike. The first time, they continued hiking. The second time, the grizzly was running at them and the man told his wife to run.

The woman told park officials she did not see the bear attack her husband. When the bear went for her, Mr Nash said, she dropped to the ground. The grizzly lifted her off the ground by the pack she was wearing, then dropped her.

The woman did not seek medical attention, Mr Nash said. Authorities said they were not prepared to identify the couple until the man's family could be notified.

Park officials later worked to clear the area of people. All trails and backcountry campsites in the area were closed and a warning sign was posted on the trailhead.

Grizzlies in the Yellowstone region have been caused growing problems for people. In June 2010, a grizzly just released after being trapped and tranquillised for study killed a man hiking outside Yellowstone's east gate. Last July a grizzly killed a man and injured two others in a night-time campground rampage near Cooke City, Montana, north east of the park.

Yellowstone and nearby surrounding areas are home at least 600 grizzlies and some say more than 1,000. Once rare to behold, grizzlies have become an almost routine cause of curious tourists lining up at Yellowstone's roadsides at the height of summer season.